An alternative sub-title for this article
could be: "When is an LED tv actually an LCD tv?". The answer would
be "always".
"LCD" stands
for Liquid Crystal Display. "LED" stands for Light Emitting Diode, as
used to show your tv is in standby or in house/garden lights, for example. There
is much misunderstanding about these two terms when used to describe
televisions, much of it down to the industry itself not making things clear. The
real danger is you may not think you are confused about it (see the final
paragraph). Here's an explanation.
All current flat-screen
televisions are of two types: plasma or LCD. Notice the absence of the term
"LED". The description "plasma" or "LCD" refers
to the panel which provides the pictures you watch. Each panel is made up of
individual picture elements called pixels. A standard definition tv panel
contains around half a million pixels, an "HD-Ready" tv panel has
around one million pixels while a "Full-HD" panel has around two
million pixels.
The pixels in a plasma
panel emit light themselves, much like the old CRT (cathode ray tube)
televisions produced light from the end of the CRT which provided the screen. However,
the pixels in an LCD panel do not produce any light themselves. They need to
have light shone through them otherwise they cannot be seen.
This is where the LED
part comes in. LEDs can be used to provide that light source behind the LCD
panel. Such tvs are simply called "LED-tvs". Previously, the light
source for LCD tvs was a panel made up of one or more CCFLs (cold cathode
fluorescent lamps: using technology like household low-energy lamps) or an
electroluminescent panel (as used in large advertising signs) which was placed
behind the LCD panel and made to glow all over with an equal brightness by
using a diffuser. You can still buy tvs like that: they're just not called
"LED-tvs".
As technology has
progressed, a panel of LEDs behind the LCD panel was found to offer an advantage
over the CCFL or electroluminescent panel. LEDs could be grouped and the brightness of each group adjusted
according to what the LCD panel was showing. Bright areas of the image caused
the LEDs in that region to shine brightly, while dark areas of the image would
cause the LEDs behind them to dim down. This improved the response of LCD
screens to black, previously one of their downfalls.
Later it was discovered
that a clever arrangement of LEDs just behind one or more edges of the LCD
panel could achieve a similar result, using some sort of mirror arrangement.
This resulted in the ability to produce extremely thin LCD tvs, especially
desirable for wall-hanging.
Thus LED-tvs are of two
types: back-lit and edge-lit. You'll see one of these descriptions in each tv's
specifications, though the differences are becoming blurred as the technology
advances.
There can be problems
with all these technologies. The back-lit CCFL or electroluminescent panel can
suffer uneven illumination, especially with larger screens when more than one
CCFL is needed - quite a disaster for the resulting picture: always check such
a set for that problem. Back-lit LED-tvs can suffer a bloom around dark areas.
The LEDs behind the LCD panel are not as numerous as the number of pixels in
that LCD panel, so dark and light areas will not match up with the groups of
LEDs exactly. Side-lit LEDs can show a glow in the corners of the screen,
especially when viewing from a wide angle. All these points are things to watch
out for when selecting a new tv.
So you can see that, if
we're to describe televisions according to the type of panel used for
displaying the image, LCD is the acronym to use. LED is just a description of
how the essential light source is provided.
Evidently it's perfectly
possible for members of the public not to know they are confused by this. I was
once told by a very knowledgeable and experienced sales assistant in a notable
tv shop about a lady who asked to see some LED televisions. When he told the
lady that all such televisions were actually LCD tvs, she would have none of
it. She told the assistant he didn't know what he was talking about and
promptly exited the shop!
